In `Shopify` I made a custom app in `php`. And now I need to make logic that will work on the `checkout` page.
In fact, I need to change the UPS delivery price conditionally, which means I need to catch or simulate the event of assigning the delivery price to the product price.
Can please tell me how I can execute my `php` code, written in `index.php`, on the `checkout` page? Or how and where can I link my `php` code to page `checkout`?
There is absolutely no information on this in the shopify documentation! In the `Shopify Dev` documentation, I've seen scripts for `wasm` - https://shopify.dev/apps/checkout/shipping-methods, but that's not what I need.
I hope very much for your help! Thanks!
